Interpretive Summary: The role of bacteria in the development of gassy bloat (excessive stomach gas) in cattle fed wheat has not been clarified. Gassy bloat in cattle often leads to death of the affected animal. Two experiments were designed to investigate the effect of grass hay and wheat on the growth of different kinds of bacteria and the development of bloat in steers. In experiment 1, certain types of bacteria were shown to produce the most gas. Other bacteria were identified as those that grew as a slimy film that is often associated in the cow stomach with bloat. In experiment 2, when diets were changed from grass hay to wheat, production of the slimy film increased. Production of the slimy film and the amount of protein in the stomach fluid were higher in the bloated steers than in the steers without bloat. Bacteria in steers with bloat were different from those in steers without bloat. This study highlighted the changes in the types of bacteria present in the stomach fluid of bloated and non-bloated cattle. The differences in the kinds of bacteria found suggest that bloat might be related to the types of bacteria present in steers fed wheat. This research is of interest to beef cattle producers and processors.

Technical Abstract:
The role of rumen bacteria in the frothy bloat complex common to cattle grazing winter wheat has not been previously elucidated. A series of in vitro and in vivo experiments were designed to elucidate the effect of fresh wheat forage on the bacterial growth, bio-film complexes, rumen fermentation end products, rumen bacterial diversity and bloat potential. In Exp. 1, six strains of ruminal bacteria (Streptococcus bovis No 26, Prevotella ruminicola ssp. 23, Eubacterium ruminantium B1C23, Ruminococcus albus SY3, Fibrobacter succinogenes ssp. S85, R. flavefaciens C94) were used in vitro to determine the effect of soluble plant protein from winter wheat forage on specific bacterial growth rate (SGR), bio-film complexes, VFA and ruminal H2 and CH4 in pure and mixed cultures with Methanobrevibacter smittii. The SGR in plant protein medium (PPM) containing soluble plant protein (3.27% nitrogen) was measured during 24-h incubation (39 deg C) in Hungate tubes under a CO2 gas phase. A pure culture of M. smittii was grown similarly, except under H2:CO2 (1:1), in a basal methanogen growth medium supplemented likewise with soluble plant protein. In Exp. 2, six rumen cannulated steers grazing wheat forage were used to evaluate the influence of bloat on the production of bio-film complexes, ruminal microbial biodiversity patterns and rumen fluid protein fractions characteristics. In Exp. 1, cultures of R. albus (P < 0.01) and R. flavefaciens (P < 0.05) produced the most H2 among strains and resulted in greater (P < 0.01) CH4 production than other co-culture combinations. Cultures of S. bovis and E. ruminantium + M. smittii produced the most bio-film mass among strains. In Exp. 2, when diets changed from Bermuda grass hay to wheat forage, bio-film production increased (P < 0.01). Bio-film production, concentrations of whole rumen content (P < 0.01) and cheese-cloth filtrate protein fractions (P < 0.05) in the rumen fluid were higher for bloated than for non-bloated steers on d 50 when grazing wheat forage. The molecular analysis of the 16S rDNA showed that two different rumen microbiota populations developed between bloated and non-bloated animals grazing wheat forage. This study highlighted that changes in digestive microbial populations between bloated and non-bloated in the rumen were observed as difference in amplicon patterns on denaturing gradient gels, suggesting that frothy bloat frequency might be related to microbial ecosystems.